Numerous ostoesynthetic procedures reduce fractures through the implantation of fasteners for fixing bone fragments. Many of these procedures require a determination of the length of a bore to be drilled or of a fasteners to be implanted in a bone. Proper bone penetration or implantation depths of fasteners are crucial, especially in small bones, small bone fragments, and in intra-articular regions where excessive penetration can damage surrounding tissues, including intra-articular cartilage.
In many modern procedures, a surgeon implants a guide wire into a bone to guide subsequent tools and fasteners, such as cannulated drills, screws, and nails. The surgeon must ensure that the guide wire penetrates the bone to a desired depth, in many cases up to, but not beyond, the distal bone cortex. Guide wire insertion is commonly performed while monitoring the guide wire's trajectory in relation to the bone with a mobile fluoroscopy unit. Kirschner wires or pins are also employed in certain procedures. Kirschner wires are similar to guide wires, but are generally thinner and have no threads.
Once the guide wire is in place, the surgeon must then determine the actual depth of guide wire implantation. Known instruments require surgeons to perform an additional step and use additional instruments after drilling in the guide wire to make this determination.
A common instrument used for measuring guide-wire implantation is described in U.S. Pat. No. 4,341,206. The instrument is a tube with a C-shaped cross-section so that its interior channel is visible along a longitudinal slit. A scale is marked on the outside of the tube, adjacent the slit. After implanting the guide wire, the surgeon must detach the drill from the guide wire and slide the tube over the exposed end of the wire until it contacts the surface of the bone. The unimplanted tip of the guide wire is thus visible through the slit. The scale on the tube is calibrated to provide a numerical reading of the penetration depth of the particular length of wire used. This numerical value is obtained by reading off the number on the scale aligned with the unimplanted guide-wire tip.
U.S. Pat. No. 5,122,146 discloses another instrument designed to measure the depth of guide wire insertion into a medullary canal of a femur. The instrument comprises a graduated hollow shaft designed to receive and secure a guide wire within the shaft. A sleeve slides along the outside of the shaft and carries a pointer that lines up with the graduations to indicate depth. According to the patent's teaching, a surgeon initially drills a guide pin into the medullary canal, then enlarges the entry hole with a hipbolt reamer, and subsequently removes both the pin and the reamer. The surgeon then inserts a bead-tipped guide wire into the instrument and then through the reamed entry hole. The surgeon slides the instrument until a part of it is flush with the proximal portion of the guide wire and locks them together. At this point, a portion of the instrument's shaft is disposed within the bone. To measure the depth of the hole and of the subsequent implant needed, the sleeve is slid down the instrument until it abuts a proper portion of the bone, which in the described case is the tip of the greater trochanter. The sleeve may be locked in place and the depth read either before or after the instrument is removed from the bone.
Several other patents teach gauges that are themselves inserted into the bone to determine the depth of a drilled hole when a guide wire is not used. U.S. Pat. No. 5,013,318 shows a depth gauge with a sliding disk on an indexed shaft. The gauge is inserted into a hole in the bone that is smaller than the disk. When the shaft is fully inserted, the surgeon may either read the last marking remaining on the outside of the bone, or may slide the disk against the bone and read the depth after removing of the gauge from the bone.
Another bone-penetration depth gauge appears in U.S. Pat. No. 4,450,834. This gauge comprises a probe that telescopes within a handle. An indicator tab is fixed to the probe and slides within a longitudinal slit made through the side of the handle, adjacent a graduated scale. The physician slides probe within the handle by sliding the tab and may thus take measurements by reading the positions of the tab against the scale.
Other known instruments guide a drill bit or a pin during implantation. Some also prevent the drilling tool from penetrating any deeper than a preset value, but these instruments demand a prior determination of the necessary preset value by procedures such as those discussed above.
U.S. Pat. No. 4,549,538, for example, teaches a pin-inserter sheath adapted to attach to a drill. A drilling guide with multiple telescoping segments retracts against a surface of the drilled tissue as the pin penetrates the tissue. No graduations are provided.
U.S. Pat. No. 5,409,493 discloses a drill guide that can be telescopically collapsed to a desired length for limiting bone penetration. A scale on an inner telescoping tube may be used to indicate the amount by which the guide has been collapsed. After determination of the required drilling depth with another instrument, the surgeon partially collapses the instrument by squeezing a handle until the length of the instrument equals the length of the drill bit less the desired drilling depth. The surgeon then begins the drilling operation through the guide until he or she reaches the selected depth.
As mentioned above, the prior art instruments for determining drill penetration or guide-wire implantation depth require surgeons to perform an additional step and operate different apparatuses. These techniques require removing the drill and either inserting a gauge in the remaining open hole, or placing a measuring device over the external portion of the guide wire. Moreover, gauges that must be inserted into an open hole are not compatible with procedures that call for drilling, nailing, or screwing cannulated instruments axially along a preimplanted guide wire, as the gauges would require the guide wire to be extracted before measurement.
The high hourly cost of operating rooms today presents a serious drawback to procedures requiring time-consuming multiple steps. Some surgeons are tempted to avoid spending time using precise measuring instruments, and instead hold a ruler up to the unimplanted portion of the guide wire or compare this portion with a second guide wire of the same length to get an approximate depth determination. Moreover, if surgeons also omit the use of a drilling guide, tissue surrounding the drilling tool can be harmed, and thin tools such as guide wires can bow, altering their insertion angle.
None of the prior art instruments provide an instantaneous, continuous, and direct reading of the drilling depth of a guide wire or other drilling tool. Known devices do not permit a surgeon, in a single step, to implant a guide wire and determine the length of a subsequent tool or fastener to be implanted over the guide wire. Moreover, previous instruments do not simultaneously protect surrounding tissue from a spinning drill bit or guide wire, support the guide wire, and provide an instantaneous depth indication without the need to make calibrations or calculations to account for the length of the tool protruding from a drill chuck.